This invention relates generally to a tool changing mechanism for a numerically controlled machine tool and more particularly to an improved automatic tool changer having a double arm construction allowing for very rapid changing of tools with a minimum of down time, thereby giving an especially short "chip-to-chip" interval.
In many common machine tools, the workpiece to be machined is placed upon a table that is mounted on the base of the machine for horizontal motion along two perpendicular axes. Any part of the workpiece thus can be brought into position to be acted upon by a tool secured to and driven by a spindle that rotates on a vertical axis above the work table and is carried by a spindle head mounted on the base of the machine for up and down motion along the vertical axis of the machine.
With the addition of numerical control, all of the motions of the machine components along all three axes can be automatically effected and controlled in accordance with a predetermined program. However, unless the machine is also equipped with an automatic tool changer by which tools can be removed from a tool storage magazine and inserted into the spindle and also withdrawn from the spindle and returned to the storage magazine, much of the advantage of numerical control is not realized.
In recent years, machine tools have been constructed with automatic tool changing mechanisms which allow a machine tool to utilize a large number of tools of various types. The machining operations are controlled by the so-called numerical control methods, and, after a particular machining action has been completed, the old tool is automatically removed from the machine spindle and placed in a tool storage magazine and a new tool is automatically taken from the tool storage magazine and placed into the machine spindle.
Machine tools equipped with automatic tool changers have been available for some time and several United States patents have been granted on such machines. Notable among those U.S. Patents are the following:
Brainard et al. No. 3,286,344 Issued Nov. 22, 1966 PA1 Brainard et al. Reissue No. Re. 25,737 Issued Mar. 2, 1965 PA1 Meyer No. 3,316,629 Issued May 2, 1967 PA1 Meyer No. 3,466,971 Issued Sept. 16, 1969 PA1 Lehmkuhl No. 3,200,492 Issued Aug. 17, 1965 PA1 Hollis No. 3,412,459 Issued Nov. 26, 1968 PA1 Anthony No. 3,161,951 Issued Dec. 22, 1964 PA1 Swanson et al. No. 3,256,600 Issued June 21, 1966 PA1 Stark No. 3,276,116 Issued Oct. 4, 1966 PA1 Wakfield et al. No. 3,465,890 Issued Sept. 9, 1969 PA1 Harmon No. 3,466,739 Issued Sept. 16, 1969 PA1 Ollearo No. 3,545,075 Issued Dec. 8, 1970 PA1 Goebel et al. No. 3,551,984 Issued Jan. 5, 1971 PA1 Anderson No. 3,811,179 Issued May 21, 1974 PA1 Noguchi et al. No. 3,822,466 Issued July 9, 1974
The British Pat. No. 1,205,104 published Sept. 16, 1970 illustrates another prior art tool changer.
While the machines disclosed in some of the aforesaid patents are known to have achieved a measure of commercial success, in all of them the unproductive time spent in changing from one tool to another is a serious production-limiting factor.
It is very desirable to effect the automatic changing of the tool within as short a time interval as possible. With a machining job requiring a large number of different machining operations involving a large number of different cutting tools, the time required to change the cutting tools inbetween each separate machining operation can add up to a considerable amount of "down time."
The problem with existing automatic tool changers is that the transfer time required to change out a cutting tool is greater than desired. This is owing to the fact that the cutting tool transfer gripping jaws and arms are constructed and arranged to require a number of mechanical steps involving movements of transfer arms which require that the machine not be operating in the cutting mode until the completion of all or a large percentage of such movements. Additionally, time is lost while a desired tool is selected from a storage magazine or returned to a specific station in the magazine for subsequent retrieval.